The present disclosure relates generally to polymer structures. More specifically, the present disclosure relates to multiple layer structures comprising a poly(vinylidene chloride) layer.
Poly(vinylidene chloride) (PVDC) has been a barrier layer in co-extruded film structures for various packaging applications. One of the difficulties of utilizing PVDC in a co-extruded structure is finding a suitable tie layer to bond the PVDC layer to other polymeric materials. Various tie layer materials such as ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA) or ethylene acrylic acid (EAA) have been used as a tie layer with PVDC for non-retortable applications. However, there are very few tie layer materials for PVDC that can survive retort application.
A good tie layer usually needs to have some miscibility with the substrate to create entanglement at the interface, or have chemical reactivity with the substrate to create chemical bonds. For retortable applications, the tie layer material should be resistant to heat sterilization, for example, at temperatures greater than about 121° C. Tie layer materials such as EVA, EMA and EAA all have melt points below 121° C. and are not able to resist mechanical deformation during steam sterilization.